The objective of this research is to obtain a basic understanding of the visual characteristics of patients with retinal diseases. Since certain retinal diseases are known to affect the foveal blue cone mechanism first, the initial phase of this overall study will focus on psychophysical analysis of the functional characteristics of the foveal blue cone mechanism in eyes of patients with early retinitis pigmentosa. Retinitis pigmentosa refers to a group of hereditary retinal degenerations in which there is a bilateral progressive loss of vision, beginning with night blindness and sometimes progressing to gradual obliteration of the visual field. The psychophysical methods are designed to test the relative roles of receptors and neural retinal organization affecting the blue cone mechanism in these patients. From these tests, we will learn more about the nature of the disease and the level in the retina responsible for the defect. It is anticipated that this research will add to our understanding of defective color vision of patients with a variety of ocular abnormalities as well as normal human color vision.